Signaling and control system for carrier telephone trunk circuits



Patented Nov. 23, 1948 SIGNALING AND CONTROL SYSTEM FOR CARRIER TELEPHONE TRUNK CIRCUITS Everhara n. B. Barteiink, Bronxville, N. Y., signor to General Telephone Corporation, New` York, N. Y., a corporation of New York Application February 20, 1947, Serial No. 729,829

(Cl. Z50-6) 7 Claims.

This invention pertains to supervisory signaling systems for use in commotion with radio or carrier current telephone toll lines'.

Where radio or carrier current telephone links are employed on toll lines interconnecting central oflices, the radio-or carrier terminal stations will in general be located at points more or less remote from the central ofiices which they respectively serve. The connection between the radio or carrier terminal station is ordinarily completed over a two-wire, two-Way low frequency circuit which is coupled through a hybrid coil to the radio or carrier current transmitter input, and also to the radio or carrier current receiver and demodu.- lator output.

It is necessary that the central olce. operator be kept advised, by means of appropriate supervisory signals, as to the status of the radio or carrier link at all times, and that she have the requisite means at her disposal at the central ofice switch board, for appropriately controlling the operation of the radio or carrier link during as well as between calls. Thus, the operator must be advised as to when a call is incoming over the radio or carrier link, and also as to when the distant central oice has disconnected; The operator upon answering the call, must have means available at the switch board for switching on the outgoing carrier of the local radio or carrier current transmitter, and for thereafter observing when the transmitter is operating and on frequency. It is also desirable that these. various supervisory signaling and control functions be carried out over the same pair of wires as is used for voice frequency transmissionbetween the'central oilce and the radio or carrier current terminal station.

'I'he present invention provides-simple and. effective circuits and apparatus for accomplishing these various operations including: a control circuit for switching the radio transmitter carrier on and off from the central ofllce; a control circuit to advise the central oce operator that an incoming call is being received bythe radio transmitter; and a. control circuit to advisev thel operator whether or not the radio transmitter is operating to provide outgoing carrier of the correct frequency.

The'invention will be described with particular reference to a radio link in a toll line interconnecting central oflice exchanges, although it will be understood that the same circuits and apparatus are equally applicable tocarrier current wire circuits, inasmuch as. the high frequency terminal equipmentis fundamentally the same in each instance, so that the supervisory signaling and circuit control problems are the same. l

The invention comprises, in general terms, a two-conductor, two-way, voice frequency circuit extending from a central oiiice to a radio station, atV which point it is linked, for voice-frequency transmission, through a hybrid coil to the input of a radio transmitter and to the output of a radio receiver. In addition to transmitting the voice frequencies, the two-conductor circuit also provides, over each conductor, a separate supervisory or control signaling circuit, between the radio station and the central ofdce., 'I'he voice-frequency circuit is metallic, While the signaling circuits employ ground return. The voice-frequency and signaling circuits are suitably isolated from one another by means of appropriately constructed and disposedlter circuits, transformers and condensers.

At the radio station, the following signaling equipment is provided: a carrier relay responsive to carrier incoming to the radio receiver; a transmitter relay for switching on the outgoing carrier of the radio transmitter; a frequency monitor and associated relay responsive to outgoing carrier of the radio transmitter for indicating when the transmitter is operating and on the correct frequency and a polarized oscillating relay energized from a, low-frequency alternating current generator under control of the transmitter relay for purposes to be explained.

'Ihe signaling and control circuit equipment provided at the central ofdce comprises: a slOwacting supervising relay for energizing a call lamp to indicate when a, call, incoming,y over the radio link, has been placed or terminated; an alternatingv current, frequency monitor signaling device, responsive to the low-frequency generator and polarized relay aforesaid, for indicating when the radio transmitter is operating and on the correct frequency; and a jack relay responsive to insertion of the operators cord plug into the toll line jack, for switching on thev outgoing carrier of the radio transmitter and for extinguishing the call lamp when the incomingy call has been an.- swered.

One conductor of thetwo-wire, voice-frequency circuit is employed as a direct current, ground return circuit, for energizing the transmitter relay from the central omce to switch on the outgoing carrier, upon insertion of. the operators cord plug in they toll line jack. The remaining conductor of the two Wire-circuit provides a direct current, ground return circuit, for` energizing thev central supervisingrrelayirom the radio station in reive-ei spon'se to incoming calls; and also as an alternating current circuit for energizing the central office frequency monitor signaling device from the radio station, when the radio transmitter is operating and on frequency. These operations are achieved, in accordance with the invention, by the application of positive or negative or alternately positive and negative voltages to the radio station end of the conductor to which the supervising relay and frequency monitor signal devices are connected at the central office. These voltages are applied to said conductor through contacts of the frequency monitor, carrier and polar relays, in accordance with the operations thereof and in such manner as to effect the various signaling functions above referred to.

The single iigure of the drawing illustrates, in circuit diagram form, a preferred embodiment of the invention.

Referring to the drawing, there is illustrated diagrammatically a radio station comprising, a radio telephone transmitter -1 and a. radio telephone receiver 2, the voice frequency input and output of which are respectively connected over circuits 3, 4, to a hybrid coil 5, provided with a line balancer 6, and thence over a circuit 1 and through transformer i to a two-wire, two-way, voice-frequency circuit 9 extending to a central otlice, and thence through transformer I thereat, to conductors II terminating at jack I2 on a switch board at the central ofdce. The operators cord I3 is provided with a plug I4, insertable in iack I2, for answering a call incoming from the radio station over the two-conductor radio circuit 9.

For advising `the central office operator as to when a-call is incoming te the radio station, there is provided thereat a carrier relay C, which responds to carrier current, indicated at I5, incoming to radio receiver 2. Also there is provided means whereby the central omce operator may switch on the outgoing carrier, indicated at I6, of radio transmitter l, said means including transmitter relay T which controls, through its armature and front vcontact T-I, a circuit I1 for switching on said outgoing carrier. 'I'he transmitter relay is energized from negatively grounded battery 19a over a circuit which includes the 'TC conductor 0f the two-wire circuit i extending to the control oice. For advising the operator as to when transmitter I is operating and on frequency, there is provided a frequency monitor I8 and associated frequency monitor relay F, which responds to the outgoing carrier as indicated at Il, when the 'carrier is being transmitted on the correct frequency.

In addition to the equipment above described, there is provided at the radio station a, low-frequency, alternating current generator 29, for generating a frequency -on the order of ten cycles lper second, as indicated, the output of this generator being connected over a circuit 2| and through an amature T-2 and associated front contact `'of the transmitter relay T, to the winding of a polarized oscillating relay O. Also there is provided a rectifier 22 for converting a source yof alternating current .23 into a. low voltage, direct current to provide a direct current -output voltage of .positive polarity between an output conductor 24 and a. .grounded conductor 25, and also t0 provide a corresponding voltage of negative polarity between an output conductor .26 and said grounded conductor 25. rslhe positive output lead 24 is wired in multiple, through ement-limiting resistors, :such as 2l, to a lbank contact of an yannacnuoo nirttlibl;

lower conductor RCY of the two-wire circuit 9 extending to the central cnice.

Referring now tov the central omce, there is provided a jack relay J, connected between the negatively grounded battery 28 and the ring conductor 29 of jack l2, this relay being energized when the operators cord plug I4 is inserted in jack I2, owing to the ground 30 connected to the ring conductor of the plug I4. There is also provided at the central oce a slow-acting vsupervising relay S, the winding of which is connected between the lower conductor RC ol.' the two-wire circuit 9, and an armature J-2 of the jack relay, the associated back contact of which is connected through a current-limiting resistor 3l to positively grounded battery 32., and theassociated front contact of which is connected through a similar resistor 33 to ground.

The supervising relay S is provided with a grounded armature S-I, the associated front contact o f which is connected through a, call lamp CL to negatively grounded battery 39. There is also provided at the central oftlce an alternating current signaling device 40, responsive to low frequency .alsternating current and comprising a Icondenser 4i connected in series with aresistance L2 to ground, the resistance 42 in turn, being connected in shunt to a frequency monitoring lamp or neon tube ML, The signaling device 40 is connected to the lower conductor RC .of the twowire Vcircuit 9.

The jack relay is provided with a second armature J--I, which is connected to the central ofce end of the upper conductor v'1 of circuit 9, this amature having a back contact connected through a low resistance 34, of about a thousand ohms or so, and thence in series to ground at 35 through a high resistance 36 of megohm or so, the high resistance being shunted by a by-pass condenser 31 of about .a microfarad capacity. The associated front contact of armature J-I is connected through a low resistance 33 of about a thousand ohms or so, to groundfat 35;

It will be observed that the lupper-conductor TC of .the two-wire circuit 9, provides a direct current path from grounded battery I9athrough the winding of relay T at the radio station, and over conductor TC to amature J-I of the normally deenergized jack relay at the central oiiice. The transmitter relay T 'is thus normally deenergized owing to the high resistance path t-o ground through the J-I armature and back contact of the,J relay through resistors 34, 36,"th'e latter, as stated, being of the `order of a megdhm -or so. -On the other hand, when the J relay is energucci, this in turn -energzes the transmitter relay -T over th'e low resistance path to ground through the J-I armature and front contact, vand low resi-stance 38 to ground at 35. Accordingly, the transmitter relay T will be energized when the operatorie cord plug vI4 is inserted in jack l2 toenergize the jack relay J.

Reverting now to .the lower conductor RC of circuit e, '11; wm .be observed that the-#central StARCH ROOM omce end of this conductor is normallyconnected through the supervising relay S to negativeA battery. 32- through the J--2 armature and back contact of` the normally deenergized jack relay I 2. On the other hand, the radio station end of conductor RC normally extends in series through the O-I armature and back contact of the normally deenergized polar relay O, and thence through the C-I amature and back contact of the normally deenergized carrier relay C, to negative battery supplied over lead 2G of rectifier 22. Although this provides a directeurrent path from the negative voltage lead 2 6v at the radio station over conductor RC to one terminal of the winding of the supervising relayA` S at the central office, nevertheless this relay is normally deenergized owing to negative battery, likewisev normally supplied to the opposite terminal of this winding from battery 32.through the J-2 armature and back contact of the jack relay.

However, upon receipt of incoming carrier I5. to radio receiver 2, the carrier relay C will operate to transfer its C-I armature from its back. to its front contact, whereupon positive voltage from the rectiier output conductor 24 will be applied to the C-I armature, and thence over conductor RC to the supervising relay S at the central oce, which will thereupon operate owing to positive battery now applied to one terminal of its winding, and negative battery from source 32 applied to the opposite terminal there-V of. The resulting operation of the supervising relay will thereupon energize the call lamp CL from battery 39 through the front contactand grounded S-I armature of the supervising relay. In this way, the, operator is apprized as to an incoming call.

When the operator answers the call by inserting. her cord plug I4 into jack I2, the jack relay J is energized as aforesaid, to transfer its JI, J-2 armatures from their back contacts to their front contacts. The supervising relay remains momentarily operated, since its winding is now grounded at the central omce through the jack relay J-2 armature and front contact, the latter being connected to ground through resistor 33. At the same time,.the transmitter relay T is energized from battery I9a, over conductor T and through the J-I armature and front contact of the jack relay,V to ground at 35 through the 10Wv resistance 38. Energization of the transmitter relay closes, through its T-I armature and front contact, the circuit I1 for switching on the carrier-IB outgoing from the radio transmitter I. Operation of the T relay also connects, through its T-Z armature and associated front contact, the low'frequency generator 20 to the oscillating relay O.

The. oscillating relay O is thereby energized fromthe low frequency source 20, alternately to switch its O-I armature between its associated back and front contacts, at the frequency of source 20. However, assuming for the moment that the outgoing carrier I6, I9 from the radio transmitter I is not on the air as yet, or is not outgoing on the proper frequency, the frequency monitor relay F will not be actuated. Under these circumstances, it will be noted that posi.

rier relay by the incoming carrier, in consequence the frequency, monitor relay F will be energized',`

lcurrentover the RC conductor, thus extinguish?!- ling the frequency monitoring lamp ML. At. the;vv

to apply, through. its F-Iy armature andfzfrp'ntA contact, a negative voltage to the front contact of the oscillating relay armature O-I, while posi-,-v tive voltage remains applied to the back contact;

thereof as aforesaid.` In this case, the oscilla.-v

tions of the O relay will put voltage reversals on,v the RC conductor extending to the central oi'llce, thus reducing substantially to zero the current flowing in the winding of the slow acting supervising relay S, which thereupon releases to extinguish the call lamp CL. At the same time.; however, alternating current at the frequencyof operation of the oscillating relay O, is causedw to flow through the alternating current frequency,-

` monitoring device 40 at the central office, thereby to illuminate the monitoring, neon lampk ML.v The operator is thus advised that carrier is outgoing from transmitter I on the proper frequency, and also that carrier is incoming to radio receiver 2 from the distant or calling station.

Whenthe operator at the distant central oflce, disconnects, the incoming carrier to the radio, receiver 2 will cease, whereupon the Acarrier relay',` C will release, to which itsC-I, C-2 armatures from their associated front to their associated, back contacts. Negative voltage therefore apa. pears on both front andback contacts of thel O -I armature of the oscillating relay 0;. theref., by to terminate thetransmission of alternating-f Sametime, the application yof negative voltage to both contacts ofthe O relay,` againl energizes the.: supervising relay S at the central office, which in,A turn energizes theV call lamp CL, thus-.advising the operator that thedistant Central oflcehasI disconnected.

If the local central omce, operator.` should re., move her cord plug I3 fromv jack I2, Whilethef: call is in progress, the transmitter relayT will release to switch oi the out-going carrier. atits, T-I armature, and also to disconnect generator 20 from the oscillating relay O at its T2 armature. Accordingly, the 4frequency monitoring lamp ML is extinguished, but the supervising relay S and the call lamp CL are energized, until4 the distant operator has disconnected, dueto the fact that the carrier relay C remains operated` until then, thereby to apply positive voltage.. through its C--I armature and front contact,` to the RC conductor.

The signaling and voice frequency circuits,` of the two-wire circuit 9. are isolated from one., another by means of the isolating transformers, 8, I0, and associated filter circuits 43,44. It willf, be noted in this connection that one winding of: each of the transformers 8, I0 has interposed at its midpoint one of the lter circuits 43,44, which. illters off to ground at 45, the, higher harmonics,4 of the alternating current from theV signaling, circuits; while the interposition of the two-winding transformers 8, II) in the voice frequency, circuits prevents the direct current signals fromv4 entering the voice frequency circuit.

Operation of the signaling circuits under the various conditions which occur may be restated as follows:

1. System idle.-At the radio station, the C relayis released, because there is no incomingofwhich the supervisingrelay S will remain en` y 7g. carrier. The T` relay is released dueV to. release,

17H-Dl cnt-the J relay at-tne connaiv once. nance, F and O relays are released. Negative-vomisaccordlnglly applied-to the RC conductor. At the opexitorscord circuit plug ls msoonnected from jack-HI. The supervising relay is released becansovnegatlve voltage is applied to both sides -of its winding terminals, that of the RC conductor one one side, and that of battery 32 through the back contact and J-l armature of the J relay, on the other. The call lamp CL is accordingly extinguished. Also the ML lampfis extinguished, because no alternating current is applied to the RC conductor.

2. Incoming calla-The C relay is energized by `the incoming carrier, and thus applies positive voltage to the RC conductor. The supervising relay is accordingly actuated to energize the 'call lamp CL,

3. 'Gail answeredFInsertlon of plug Il in jack l2 energizes the J relay. This in turn actuates the 'I' relay to switch on the outgoing carrier from the radio transmitter, and also to energize the oscillating relay from generator 20,

If the outgoing carrier is not on the air, or is not on frequency, the F -relay will remain vdcenergized, in which Vcase positive battery will be applied to the RC conductor on both contacts .of theo relay, since the carrier relay C remains operated by the incoming carrier. Hence, no altemating current is applied to the RC conductor and the monitoring lamp ML remains tleerreri gleed.- Qntheother hand, the supervising relay remains-energized' to ground through the J-'2 armature and associated iront ccntactof the J relay. The call lamp CL thus remains lighted.

When the outgoing carrier is .on the air, at the correct frequency, theF relay will operate, to put negative voltage on the front contact of the O relay, the backV contact of which receives positive battery as aforesaid. Square-wave alternating current voltage is thus applied iso-"the ,RC conductor, which energlzcsthemonitoring lamp ML at the central office, but deenergizes the S relay and with it the call .lamp CL, which is extinguished. Y

4. Disconnect-Release of the circuit by the distant central office will switch' off the incoming carrier and thus release the C relay. This restores negative battery to both contacts of the f' O relay,to extinguish the monitoring lamp ML at the central cfllne, and to energize the S relay and with it the CL lamp which relights, thus signaling the central: oce operator to disconnect'. When the operator removes her corfd plug from jack I4, the J relay will release to extinguish the CL lamp by application of negative voltage to both terminals of the S relay winding, which releases. This also releases the T relay which in turn releases the F' andO relays, thus restoring the system to its idle condition.

If the .operator-pulls the plug Il before the incoming carrier is on', the J, T, .F and 0 relays will release. The C relay will remain actuated by theincoming carrier, and hence .will apply positive battery to the'RC conductor. The ML lamp willbe. extinguished, but the S relay will' be energized and with it the CL lamp, until the distant operator has disconnected.

I claim:

l. In a communication system: a carrier current transmitter and receiver; a two-conductor circuit connecting the same to a central ofllce; a carrier relay responsive to carrier current ing; switciiing on carrier. current outgoing transmitter; a supervislngrel'a'y at the omce; means including said ycarrier relay and one lconductor of said two-conductor circuit, lff

energizing said supervising relay ln response to incoming carrier; and means including tlie remaining conductor of said two-conductor circu-it and switching means at the central omce for energizing said transmitter relay to switch on the outgoing carrier.

2. In a communication system: a carrier current transmitter and receiver; a two-conductor circuit connecting the same to a central ofdce; a carrier relay responsive to carrier current lncoming to said receiver; a transmitter relay for switching on carrier outgoing `from said transmtter; a supervising relay at the central office and a call lamp responsive thereto; means in` cluding said carrier relay and one conductor v1:71' said two-conductor circuit, for energizing said supervising relay and call lamp in response to inJ coming carrier; and means including the remaining said conductor, a jack having a sleeve conductor, a jack relay connected to said sleeve conductor and an operators cord plug at the central ofllce, for energizing said transmitter re' lay upon insertion of said plug in said jack, thereby to switch on carri-er current outgoing from said transmitter.

3. In a communication system: a carrier current transmitter and receiver; a two-conductor circuit connecting the same to acxgrglofce'; a carrier relay'responsive'to car r current in coming to said receiver; a transmitter relay fo switching on carrier current outgoingirom said transmitter; a frequency monitor havinga, frequency monitor relay connected in its'output and responding to said outgoing carrerwhen of. a preselectedfrequency; a source of low-frequency alternating current and a polar relay energizable therefrom upon actuation of said transmitter relay; a supervising relay, a jack relay and an alternating current signaling device at the centralollce; means including contacts o'f said carrier and polar relays, and a rst conductor of said two-conductor circuit, for energizing said supervising relay in responseto incoming carrier; means including said jack relay and the second conductor of said two-conductor circuit, for energizing said transmitter relay to switch on' the outgoing carrier; and means including con--v tacts of said frequency monitor, carrier and polar relays and said rst conductor, for extinguishing said supervising relay and energizing said alternating current signalingdevice while car= riez' current vis incoming to said receiver and concurrently outgoing from said transmitter onsaid preselected frequency. j

4. In a. communication system: a carrier current transmitter land receiver; a two-conductor circuit connecting the same to a central omce; a carrier relay responsive to carrier. current'inr` coming to said receiver; a transmitter relay 'for switching on carrier current outgoing from said transmitter; a frequency monitor havinga frequency monitor relay connected in its output, and responding to said outgoing carrier when of a preselected ,frequency; a polar relay energizable from a low-frequency alternating current source in response to actuation of saidtran'smittel' relay; a supervising relay and a low-frequency signaling device connected. to anrst con-'- ductor of said two-conductor circuit at the cen'- tral o'fdce, the opposite end of said nrst vconductor coming to said receiver; a transmitter relay for being connected to an armature of said polar relay, said armature having back and front contacts connected respectively to a pair of armatures of said carrier relay, said carrier relay armatures having back contacts connected to a negative voltage source, and front contacts respectively connected to a positive voltage source and to an armature of said frequency monitor relay, the latter said armature having back and front contacts respectively connected to said positive and negative voltage sources; and means including a jack relay at the central omce and the second conductor of said two-conductor circuit, for energizing said transmitter relay and for concurrently switching a winding terminal of said supervising relay from a negative voltage source to ground at the central office.

5. In a communication system: a carrier current transmitter and receiver; a first speechfrequency circuit coupled to the transmitter input and to the receiver output through a hybrid coil; a transformer coupling said speech-frequency circuit to a two-conductor circuit extending to a central ofce; a transformer coupling said two-conductor circuit to a second speech-frequency circuit thereat; each said transformer including a winding connected in series with a condenser between said two conductors, thereby to provide separate, direct current signaling paths over the individual conductors and a speech-frequency circuit over said conductors jointly; a carrier relay responsive to carrier current incoming to said receiver; a transmitter relay for switching on carrier current outgoing from said transmitter; a supervising relay at the central omce; means including said carrier relay and a rst said conductor, for energizing said supervising relay in response to incoming carrier; and means including the second said conductor and switching means at the central oflice, for energizing said transmitter relay to switch on the outgoing carrier.

6. In a communication system: a carrier current transmitter and receiver; a first speech-frequency circuit coupled to the transmitter input and to the receiver output through a hybrid coil; a transformer coupling said speech-frequency circuit to a two-conductor circuit extending to a central office; a transformer coupling said twoconductor circuit to a second speech-frequency circuit thereat; each said'transformer including a winding connected in series with a condenser between said two conductors, thereby to provide separate, direct current signaling paths over the individual conductors and a speech-frequency circuit over said conductors jointly; a carrier relay responsive to carrier current incoming to said receiver; a transmitter relay for switching on carrier outgoing from said transmitter; a supervising relay at the central omce and a call lamp responsive thereto; means including said carrier relay and a rst of said conductors, for energizing said supervising relay and call lamp in response to incoming carrier; and means including the remaining said conductor, a jack, and associated jack relay and operators cord plug at the central oice, for energizing said transmitter relay upon insertion of said plug in said jack, thereby to switch on carrier current outgoing from said transmitter.

7. In a communication system: a carrier current transmitter and receiver; a first speech-frequency circuit coupled to the transmitter input and to the receiver output through a a transformer coupling said speechrequency circuit to a two-conductor circuit extending to a central omce; a transformer coupling said twoconductor circuit to a second speech-frequency circuit thereat; each said transformer including a winding connected in series with a condenser between said two conductors, thereby to provide separate, direct current signaling paths over the individual conductors and a speech-frequency circuit over said conductors jointly; a carrier relay responsive to carrier current incoming to said receiver; a transmitter relay for switching on carrier current outgoing from said transmitter; a frequency monitor and associated frequency monitor relay responsive to said outgoing carrier when of a preselected frequency; a source of lowfrequency alternating current and a polar relay energizable therefrom upon actuation of said transmitter relay; a supervising relay, a jack relay and an alternating current signaling device at the central omce; means including contacts of said carrier and polar relays and a first of said conductors, for energizing said supervising relay in response to incoming carrier; means including said jack relay and the second of said conductors, for energizing said transmitter relay to switch on the outgoing carrier; and means including contacts of said frequency monitor, carrier and polar relays, and said rst conductor, for extinguishing said supervising relay and energizing said alternating current signaling device while carrier current is incoming to said receiver and concurrently outgoing from said transmitter on said preselected frequency.

v EVERHARD H. B. BARTELINK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,528,011 Demarest et al Mar. 3, 1925 1,688,452 Demarest et al Oct. 23, 1928 1,688,453 Demarest et al. Oct. 23, 1928 1,688,454 Demarest et al. Oct. 23, 1928 2,231,636 Pruden Feb. 11, 1941 2,265,056 Bowers Dec. 2, 1941 2,280,420 Chappell Apr. 21, 1942 2,425,495 Trevor et al Aug. 12, 1937 l Disclaimer 2,454,498.Everhdrd H. B. BarteZtnk,Bronxv11e,N. Y. SIGNALING AND CON- TROL SYSTEM FOR CARRIER TELEPHONE TRUNK Cmcm'rs. Patent dated Nov. 23, 1948. Disclaimer flled Nov. 8, 1950, by the assignee, Automatic Electric Laboratories, I nc. Hereb enters this disclaimer of claims 1 and 2 of said patent.

[ ctal Gazette December 5, 1.950.] 

